The overall goal of this project is to a) determine the location of the GnRH-receptor producing neurons; b) determine the identity of the neurotransmitters in the GnRH-receptor synthesizing neurons and whether the relative amounts of GnRH-receptor mRNA change in response to estradiol. 2) Identify the GnRH-mediated effects on hippocampal neurons. 3) Identify the second messenger systems which transmit the GnRH signal to the inside of the hippocampal target neurons. 4) Identify the norepinephrine neurons which mediate estradiol positive feedback actions. a) to determine precisely which noradrenergic cell groups project to the GnRH perikarya and to the GnRH axon terminals in the median eminence; b) to determine if these noradrenergic neurons contain steroid hormone receptors; c) to determine whether the gonadal steroids cause a change in the mRNA encoding for tyrosine hydroxylase. This combination of morphological, physiological and molecular biological approaches will provide detailed information on the nature of the effects of GnRH in the hippocampus and will reveal mechanisms by which the GnRH neuronal system is regulated. Together, the results will be important for our basic understanding of how the brain participates in the regulation of hormonal homeostasis and may provide clues for treatment of disorders caused by a central failure to maintain an adequate GnRH release.